I couldn't find any external documentation of the stabs either so I resorted
to looking at the dbx sources. The Berkeley dbx sources are freely
available; the file that processes stabs is "stabstring.c". I'll mail
you a copy of that file. It takes a little work but you can deduce everything
from the source.

As far as I can tell, ULTRIX dbx is pretty close to Berkeley dbx so
looking at Berkeley dbx sources will probably suffice to answer questions
about what ULTRIX dbx accepts.

On the other hand, Sun has made a number of dbx extensions, including
some extensions to the stabs. You'll probably have to talk to Sun to
get more info.

I don't know anything about Sequent's dbx.

If anyone has stab documentation other than the dbx sources, I'd be
interested too.